While most flex-fuel engines are optimized for gasoline, few are truly optimized to run on ethanol blends. Ricardo Inc. recently introduced an Ethanol Boosted Direct Injection (EBDI) flex-fuel engine that is a game-changer: It is optimized for both fuel types, and more importantly, can handle higher ethanol content blends. EBDI technology not only facilitates dramatic engine downsizing, it also allows those flex-fuel engines to approach efficiency levels of diesel powertrains, but at a much lower cost.

The EBDI engine allows truly flex-optimized engines to deliver the best possible performance and fuel efficiency from whichever gasoline-ethanol mix is selected by the driver. Ultimately, no matter what blend of fuel, the engine will always be running at an optimal level, says Ricardo. It delivers diesel-like torque along with reduced emissions, lower engine mass and reduced cost. EBDI controls the fueling, the spark timing, and the EGR rate.

Ricardo has partnered with Growth Energy, a national organization representing U.S. ethanol producers, to demonstrate the market-readiness of the EBDI technology. The company began with a General Motors (GM) naturally aspirated gasoline 3.2-liter V6 as its base engine, which was then modified to optimize ethanol performance. Two GMC Sierra 3500 HD pickup trucks — usually powered by either a 6.0-liter V8 gasoline or a 6.6-liter diesel powerplant — have been repowered with the optimized, much smaller 3.2-liter V6 EBDI flex-fuel engine to serve as demonstration vehicles.

“The EBDI engine turns the gasoline-ethanol equation upside down,” says Kent Niederhofer, Ricardo president. “It has the performance of diesel, at the cost of ethanol, and runs on ethanol, gasoline, or any blend of both.”

High-efficiency energy conversion unleashes efficiency gains
Full optimization of current flex-fuel engine systems, such as the GM 2.0-liter Ecotec or Ford 3.5-liter EcoBoost, would require that the engine be able to withstand much higher cylinder pressures than usual. Simply put, these engines do not make full use of the properties of ethanol.

For aspirated, flex-fuel, spark-ignition engines, there’s a conflict of interest between burning gasoline with an octane rating of less than 100, and ethanol, with an octane rating of approximately 110. A compression ratio high enough to exploit ethanol properly makes it unfeasible for gasoline. Consequently, full power and torque potential is not realized when burning an ethanol blend. In addition, fuel economy suffers too.

“In the past, when people have created flex-fuel engines, they have taken the gasoline engine and converted it to burn varying degrees of ethanol,” says Niederhofer. Because ethanol has only two-thirds of the energy content of gasoline on a per-gallon basis, fuel economy has suffered, leading to customer dissatisfaction.”

EBDI technologies leverage the two advantages of ethanol — higher octane and higher heat of vaporization — with advanced control algorithms that optimize operation for varying gasoline vs. ethanol content, says Ricardo. For example, the EBDI engine runs the engine's twin turbos on boost at nearly all engine speeds; the GM 2.0-liter Ecotec and Ford 3.5-liter EcoBoost engines only run turbo boost under heavier loads.

The Street: Proving Ground for Flex-Fuel Engine Optimization

Ricardo Inc.’s EBDI engine (left) will be used in two repowered GMC Sierra 3500 HD trucks (right) to demonstrate its advantages compared to the pickup’s conventional 6.0-liter gasoline and 6.6-liter diesel powertrains. No matter what blend of fuel is being used, the EBDI engine will always be running at an optimal level, says Ricardo.

Key EBDI engine specifications include:

3.2L direct injection V6 (V6 3.2l SIDI twin turbo).

Integrated exhaust manifold (IEM).

External exhaust gas recirculation (EGR) system for exhaust gas.

Temperature and knock reduction (EGR boost).

Advanced boosting concepts.

Homogeneous operation at high load for emissions compliance.

Optimized control algorithms for improved performance from regular pump gasoline through E85

Ricardo's ethanol optimization engine capitalizes on ethanol's higher octane rating. The EBDI engine’s total Brake Mean Effective Pressure (BMEP), a measure that compares the power output of dissimilar engines, is 35 bar when running on ethanol compared to 30 bar running on gasoline. In contrast, many of today's production car and light-truck engines achieve a BMEP of just 18 to 22 bar.

This enables the EBDI engine to suffer less of a mileage decrease when running on ethanol blends instead of straight gasoline — a decrease of only 15 to 20 percent, compared to 33 percent experienced by the other less-optimized flex-fuel engines. This advantage corresponds closely the cost of ethanol compared to gasoline, while providing considerably more power without loss in performance.

Ethanol direct injection also provides better charge cooling than gasoline, as a result of the higher heat of alcohol vaporization, thus reducing the work of compression and more engine net output and efficiency. Since ethanol is a fuel and not a charge diluent, more power and torque can result for a given level of boost in comparison to cooled EGR.

EBDI has the ability to take full advantage of ethanol’s properties of high octane and latent heat of vaporization to deliver near-diesel levels of engine efficiency at substantially reduced cost. According to Ricardo, the optimization of both octane and ethanol combustion yields a number of benefits, namely:
• Advanced control algorithms allow the EBDI engine to offer fully optimized flex-fuel performance on any blend of fuel ranging from standard pump gasoline through to E85 fuel.
• Engines can be downsized by the order of 50 percent, compared to current powertrains, without loss of performance.
• The new EBDI engine will cost approximately $4,500 as compared to current pickup diesel powerplants, which can cost several thousands more.
• Reduced engine cost and complexity, compared to diesel engines, enables more straightforward engineering, lower warranty risk and reduced cost of ownership.
• Based on engine test work already carried out in gasoline comparisons, the EBDI engine experienced up to 30 percent mileage improvement with no loss of power or performance. Mileage was marginally less in tests comparing diesel to ethanol blends; however, the small decrease is offset when fuel prices and engine costs are factored in.
• EBDI technology is scaleable and can be applied to engines that could be used in a mid sized car all the way through to a Class 6 truck.
• The increased availability of ethanol blender pumps in the future will allow the consumer to choose the best blend based on vehicle type, expected use and fuel cost.
Ricardo's ethanol optimization engine capitalizes on ethanol's higher octane rating.

EBDI technology leverages advanced technologies
“We took the stock V6 and redesigned every component to get diesel-like performance out of an engine that was originally designed to be lightly turbocharged,” explains Rod Beazley, director of the Spark Ignited Engines Product Group for Ricardo. “We employ two parallel, sequential turbochargers. The high level of turbocharging lets us achieve the high cylinder pressures that ethanol enables.”

“We had to work on the bottom end and on the crank, and in order to get enough of ethanol into the engine, we had to use two fuel pumps,” he adds. “Also, an integrated manifold with charge air coolers and EGR coolers help cool down the combustion. Although our block and heads look unchanged from the outside, inside they are highly modified with structural changes to support the higher cylinder pressures. In addition, we employ a high-voltage ignition system to ignite the large amounts of ethanol.”

Future Applications

Diesel engines today run about 17:1 compression ratio, which is trending down because of emission regulations, while this engine’s compression ratio is closer to 11: 1.

“Compression ratio is a function of two things: geometric compression ratio and boosting pressure,” says Luke Cruff, the chief engineer for the Ricardo Gasoline Product Group. “The turbochargers and other variable devices can adjust the boosting pressure which allows you to have different effective compression ratios.”

EBDI technology is also scalable — it can be applied to larger or smaller vehicles, such as General Motor's Cruze, to deliver optimized performance with further downsized engines. (Image — General Motors Corp.)

Beazley says that the EBDI engine incorporates advanced technologies such as direct injection, variable valve timing, optimized ignition and advanced exhaust gas recirculation to help squeeze out more power than is possible with gasoline.

Several key strategies integral to EBDI methodology include:
• Sophisticated boosting technology is provided by two BorgWarner singlescroll K04 turbochargers with water-cooled bearing housings. Intake manifold volume was reduced by 25 percent to ensure good transient response. In addition, the electronic throttle was sized for the turbos. Crankcase ventilation was also modified to operate under boosted conditions and increased blow-by levels.
• Optimized fuelling strategy and combustion control. The EBDI engine management system employs a Bosch DI Motronic MED9 engine control unit and other advances keyed of ethanol blends.
• Effective compression ratio and in-cylinder conditions are matched precisely to those required for optimal performance and efficiency. Some of the modifications featured in the EBDI engine include the crowning of cylinder heads to improve flow efficiency, high-pressure injector placement and a cylinder head-mounted, high-pressure fuel pump; redesigned pistons and connecting rods to provide durability to handle increased cylinder pressures; enhanced camshaft profiles to better handle the turbocharged transient response; and larger exhaust valve springs handle the higher back pressure resulting from the turbocharger.
• Any need for complex aftertreatment technology to meet current or planned emissions regulations is avoided. Expensive aftertreatment is not necessary with the EBDI engine, yet compared to conventional diesel powerplants, emissions in an EBDI gasoline-fueled application reduced tailpipe carbon dioxide (CO2) emissions by more than 10 percent. When ethanol blends were used, the advantage over diesel widened.

Developed on test beds, proved in the real world
The U.S. Environmental Protection Agency has announced it is considering whether to raise the ethanol blending limit; it has also begun the process to craft the labeling requirements that will be necessary should the blending limit be raised. While testing continues, the results of two recent tests indicate that engines in newer cars likely can handle an ethanol blend higher than the current 10 percent limit.

More than innovative technology is at stake. “Ethanol is the only renewable fuel that is ready to displace more foreign oil,” adds Gen. Wesley K. Clark (Ret.), co-chairman of Growth Energy. “If we are ever to achieve the energy independence that is vital to the economic and national security of our nation, we must begin to put more ethanol into our fuel tanks.” He adds that future ethanol fuel production will be derived from renewable cellulosic feedstocks, which will facilitate an increase in the volume of ethanol while avoiding competition with foodstuffs.

Ricardo test bed evaluations show that the EBDI engine delivers significant fuel-efficiency improvements without compromising performance, in particular while operating on high ethanol blends. “The reason we are using the flex-optimized EBDI engine demonstrators is that, while the engine test results speak for themselves, there is no substitute for experiencing the uncompromised performance and fuel efficiency that can be delivered from whichever gasoline-ethanol mix is selected by the driver when next stopping for fuel,” adds Beazley.

By early fall of 2010, the repowered Sierra pickups will complete a range of real-world tests that include extreme climate conditions from arid, desert situations to below-zero temperatures, as well as city stop-and-go driving. Ricardo is aiming at 2015 as a target for production-series deployment.

(Editor’s Note: Ricardo acknowledges the contributions from a number of automotive OEMs to the development of the EBDI engine. These include Behr, Bosch, Delphi, Federal Mogul, Grainger & Worrall Castings, and Honeywell.)